Hydraulic asphalt concrete is one of the important materials for interior core walls or face panel construction, and it has been widely used in hydraulic engineering, such as reservoirs, dams, or hydropower stations. The mix proportion of hydraulic asphalt concrete is vital for the construction quality of hydraulic asphalt concrete, and the construction quality of asphalt concrete core wall can be ensured by optimizing the content of hydraulic asphalt, the amount of filler, and the aggregate grading index. Because of the traditional single factor analysis method, the selection of the mixed proportion of hydraulic asphalt concrete is time-consuming and laborious, and the results are not satisfactory. The orthogonal experimental design method is applied to the mix proportion optimization of hydraulic asphalt concrete, and the results are processed using range and variance analysis methods to analyze the influences of different oil-stone ratios, filler dosage, and grading index on the optimization efficiency of the mix proportion of hydraulic asphalt concrete. The optimal mix proportion of hydraulic asphalt concrete was obtained using the oil-stone ratio, filler dosage, and grading index as independent variables, and the porosity and separation of asphalt concrete as dependent variables. The results indicate that the orthogonal experimental design method is helpful in improving the optimization efficiency of the mix proportion of hydraulic asphalt concrete.